Capabilities of multi-pinhole SPECT with two stationary detectors for in vivo rat imaging

Abstract

We aimed to investigate the image quality of the U-SPECT5/CT E-Class a micro single-photon emission computed tomography (SPECT) system with two large stationary detectors for visualization of rat hearts and bones using clinically available 99mTc-labelled tracers. Sensitivity, spatial resolution, uniformity and contrast-to-noise ratio (CNR) of the small-animal SPECT scanner were investigated in phantom studies using an ultra-high-resolution rat and mouse multi-pinhole collimator (UHR-RM). Point source, hot-rod, and uniform phantoms with 99mTc-solution were scanned for high-count performance assessment and count levels equal to animal scans, respectively. Reconstruction was performed using the similarity-regulated ordered-subsets expectation maximization (SROSEM) algorithm with Gaussian smoothing. Rats were injected with ~ 100 MBq [99mTc]Tc-MIBI or ~ 150 MBq [99mTc]Tc-HMDP and received multi-frame micro-SPECT imaging after tracer distribution. Animal scans were reconstructed for three different acquisition times and post-processed with different sized Gaussian filters. Following reconstruction, CNR was calculated and image quality evaluated by three independent readers on a five-point scale from 1 = “very poor” to 5 = “very good”. Point source sensitivity was 567 cps/MBq and radioactive rods as small as 1.2 mm were resolved with the UHR-RM collimator. Collimator-dependent uniformity was 55.5%. Phantom CNR improved with increasing rod size, filter size and activity concentration. Left ventricle and bone structures were successfully visualized in rat experiments. Image quality was strongly affected by the extent of post-filtering, whereas scan time did not have substantial influence on visual assessment. Good image quality was achieved for resolution range greater than 1.8 mm in bone and 2.8 mm in heart. The recently introduced small animal SPECT system with two stationary detectors and UHR-RM collimator is capable to provide excellent image quality in heart and bone scans in a rat using standardized reconstruction parameters and appropriate post-filtering. However, there are still challenges in achieving maximum system resolution in the sub-millimeter range with in vivo settings under limited injection dose and acquisition time.

Performance Evaluation of a Preclinical SPECT Scanner with a Collimator Designed for Medium-Sized Animals

“…The GP-MSA collimator achieved a high sensitivity of 790 cps/MBq, which is comparable with previously reported values for general-purpose mouse type (GP-M) collimators (847 cps/MBq) [ 19 ]. The spatial resolution was 2.5 mm, thereby indicating that the spatial resolution of collimators roughly corresponded to each aperture diameter [ 18 , 19 , 21 , 32 ]. We included relatively low concentrations of 0.1 MBq/mL in our phantom experiments, because the amount of tracer that can be administered as well as the scan duration is limited in a busy in vivo animal experiment set-up with a high throughput.…”

“…For example, the short-axis size of a rabbit heart is approximately 20 mm. The size of the cFOV of the collimator for rats is 28 mm [ 18 ], thereby insufficient to visualize any uptake of the rabbit's heart without bed motion. When qualitative evaluation is conducted in SPECT images, ratios of the target to the normal organs such as the blood pool and muscles are often used.…”

“…U-SPECT5/CT E-class (MILabs, Utrecht, The Netherlands) was used for SPECT imaging, displayed in Figures 1(a) and 1(b) . The system performance using dedicated collimators for mice and rats had been reported elsewhere [ 18 , 19 ]. Briefly, U-SPECT5-E was developed as a cost-effective substitute of the conventional U-SPECT5 system, which is also an ultrahigh-resolution SPECT system for preclinical imaging of small animals.…”

“…A centrally located collimator with multipinhole configuration allows the acquisition of SPECT images in a spiral step mode using an automated xyz stage [ 22 ]. To strive for cost effectiveness, U-SPECT5/CT E-class is built without the bottom detector [ 18 , 19 ].…”

Performance evaluation of a preclinical SPECT/CT system for multi-animal and multi-isotope quantitative experiments

“…We have herein studied the performance of the U-SPECT 6 E-class (MILabs, The Netherlands) with two stationary detectors and a multipinhole collimator, which might be changed for different animal sizes and image quality requirements 6 . The most important characteristics of the system, such as sensitivity, spatial resolution and contrast-to-noise ratio, have already been published for a set of collimators and for technetium-99 m ( 99m Tc), the most widely used gamma radioisotope 6 , 7 . However, a complete evaluation including additional collimators as well as results for radiotracers different from 99m Tc has not been published yet.…”